In the process of color lithographic printing, as method for preparing a color proof from plural sheets of black-and-white halftone dot images obtained by color separation and halftone dot image conversion, the overlay method and the surprint method are conventionally known, which are methods of forming color images by the use of a photopolymer or a diazo compound.
The overlay method is advantageous in that it is very simple, HAS a low production cost and can be used only by overlaying four-color (subtractive primaries and black) film sheets. However, it is disadvantageous in that the overlaying of the film sheets causes a gloss, which gives a texture different from that of the print.
The surprint method is a method in which colored images are superposed on the same support. This method is known to include methods in which the colored images are obtained by toner development that utilize adhesive properties of a photopolymerizable material, as disclosed in U. S. Pat. Nos. 3,582,327, 3,607,264, and 3,620,726.
Another method is known in which transfer is made on a support by the use of a light sensitive coloring sheet, followed by exposure and development to form an image, and thereafter another coloring sheet is superposed thereon, followed by repetition of the same process to prepare a color proof, as disclosed in JP-B 47-27441 (herein, the term, JP-B means examined and published Japanese Patent) and JP-A 56-501217 (herein, the term, JP-A means unexamined and published Japanese Patent Application). Still another method is known in which, using light sensitive coloring sheets, corresponding color separation films are exposed and developed, and the resulting respective colored images are transferred and formed on the same support, as disclosed in JP-A 59-97140. As toners and as colorants for the coloring sheets, used to form these images, the same coloring materials as used in printing inks can be used. Because of this advantage, the resulting color proof displays a color tone resembling that of the print.
In these methods, however, images must be superposed and transferred in the process of preparing a color proof, and there are disadvantages that operation thereof takes a relatively long time and they result in a high production cost. As methods that have eliminated such disadvantages, a method of preparing a color proof by the use of a silver halide color photographic material provided on a white support is disclosed in JP-A 56-113139, 56-104335, 62-280746, 62-280747, 62-280748, 62-280749, 62-280750 and 62-280849. In the method, plural sheets of color-separated black-and-white halftone dot images, converted into halftone dot images which are color-separated from a color original, are successively photographically printed on a sheet of color photographic paper by contact printing or the like, followed by color development, and a color image formed of dyes imagewise produced from couplers upon the color development is used as a color proof. However, this technique has a problem that varying the dot percentage to make a color image resemble a print results in an unwanted density increase in the white background of the image, leading to unacceptable coloring of the background. This technique further has the disadvantage that an attempt to make a color image resemble the print results in an insufficiency in the density of black images such as text compared to that of the print and, on the other hand, any means taken to increase this density so as to make a black image such as text have a density resembling that of a print brings about a low resemblance of the print to the color image, making it difficult to satisfy both at the same time.
JP-A 1-260629, 61-233732 and 4-1632 disclose a silver halide color photographic material having four emulsion layers comprised of Y, M, C and Black layers which are different in spectral sensitivity from each other. However, there is described no method for solving the above problems with respect to the density increase of the white background when varying the dot percentage to resemble the print. JP-A 8-304960 discloses a silver halide photographic material containing a pigment having an average primary particle size of 0.25 .mu.m or more. However, nothing is described therein, with respect to the density increase of the white background when varying the dot percentage to resemble the print. It is further described that the average primary particle size is preferably within the range of 0.26 to 0.30 .mu.m and only titanium oxide having an average primary particle size of at most 0.28 .mu.m is exemplified.